Presently, tube materials commonly used by manufacturers of heat exchangers are standard AA3003, or so-called long-life 3005 alloy. These are also the most commonly used materials in manufacturing processes, including Controlled Atmosphere Brazing method (CAB). The long-life 3005 alloy is a standard alloy AA3005, produced with a special process to increase the corrosion resistance of the material, which may be used in heat exchangers etc.
However, the mechanical strength of such materials does not meet the present requirements of the heat exchanger manufacturers, since heat exchanger manufacturers of today desire to produce heat exchangers comprising thinner tubes, which results in heat exchangers with lighter weight.
In the manufacturing of said tube materials, a much overlooked, but increasingly important, property is the ability of the material to resist sagging. Sagging is the ability of the material to resist deformation at brazing temperatures, imposed by the weight of the formed sheet material during the brazing process. Typically, sagging increases as the thickness of the manufactured material decreases. At the same time thinner thickness of the manufactured material requires improved resistance against corrosion attack, which corrosion attack may cause perforation of the manufactured material.
U.S. Pat. No. 6,019,939 discloses an aluminium brazing sheet, comprising 0.7 to 1.5 weight % Mn, 0.5 to 1.0 weight % Cu, less than 0.15 weight % Si, less than 0.8 weight % Mg, and optionally V, Cr or Ti and unavoidable impurities. According to U.S. Pat. No. 6,019,939 the preferred amount of Mn is 0.8 to 1.2 weight % and all examples discloses a maximum of 1 weight % Mn. This content of Mn will not produce the desired sagging resistance. Furthermore, it will also not give the maximum strength or corrosion protection that can be obtained by using a higher amount of Mn. The teachings of this patent also points away from using Zr as an additive.
JP 8246117 discloses an aluminium alloy of a high strength, used in brazing sheets for heat exchangers. The preferred Si content of this alloy is 0.3 to 0.7 weight %. This amount of Si is too high to provide the required corrosion resistance of the brazing sheet.
U.S. Pat. No. 6,465,113 discloses an aluminium alloy brazing sheet for vehicles, comprising a four layered structure consisting of an aluminium alloy core, a filler alloy on one side of the core, a sacrificial anode material on the other side and an intermediate layer between the core and the sacrificial anode material, said intermediate layer being composed on an aluminium alloy having 0.1 to 0.5 weight % Si, 0.2 to 0.8 weight % Fe, 0.5 to 2.0 weight % Mn, and 0.4 to 1.0 weight % Cu, and optionally containing up to 0.3 weight % Zr. The balance is aluminium and unavoidable impurities. The composition is used as a thin intermediate layer and will therefore not, and is not intended to, provide a required strength to the obtained product. The silicon content in the alloy is also too high to give a desirable corrosion resistance.
WO02070189 discloses an aluminium brazing sheet, particularly suitable for charge air cooler applications, wherein the core comprises <0.2 weight % Si, 1.3-1.7 weight % Mn, 0.4-0.8 weight % Mg, 0.3-0.7 weight % Cu, <0.2 weight % Ti and 0.05-0.2 weight % Zr. This alloy is used for vacuum brazed heat exchangers and receives its strength through the high content of Mg. However, since the content of Mg is high, CAB-brazing of these alloys is very difficult due to a reaction between Mg and the flux.
Thus, there is a need for a new aluminium alloy with an improved ability to withstand corrosion and sagging, while having a high strength, when used to manufacture brazed products from said alloy.